Power reduction/Shock Cooling

[snippyfsxer]

I frequently run into the rule of thumb that says you shouldn't reduce your MAP more than 3 inches per minute during the descent (cowl flaps closed) to avoid shock cooling.

[Ivan]

CalClassic prop + panel combo might have implemented this but i haven't tested that.

The Yak-18T can only overheat

[Brett_Henderson]

Modern metallurgy, has made this less of a problem.. and since airplanes for hire have mandatory rebuild times that expire before much damage can show up.. some people even ignore it altogether.

Talk to an AP guy though.. he'll tell you that there are reasons that some engines use more oil than others.. and that cracked cylinders aren't just random events.

A well thought out descent accomodates gradual power reduction (I shoot for 1" per minute) without any inconveniences.

[Fozzer]

...maybe its just funny-old me...

...but in all my Flight Sims I automatically apply Carburettor Heat and/or close the Engine Cowls BEFORE I drastically reduce power, or close the throttle for a landing, to avoid shock-cooling my engine(s) and/or generating Carburettor Ice.

Its something which I now do without even thinking about it, on all my Air Cooled Piston Engines.

Its engrained in my list of; "Important things to do (before I die!)" pasted on the Panel in front of me... ...!

Its just one of those dangers which I am always seem to be aware of!... ...!

Paul...G-BPLF... 8-)

[Brett_Henderson]

Yeah..

[snippyfsxer]

[quote]Yeah..

[Fozzer]

[quote][quote]Yeah..

[Brett_Henderson]

In many cases, carb-heat also means by-passing the air-filter.. so there's the risk of ingesting debris.

I have the AccuSimm  B377.. It has very complex intake management.. You have to control whether or not forced-air is even used.. then you control the forced air directed to the inter-coolers (they're used to reduce the heat from turbo/super-charging) (the B377 has both).. and of course the carb-heat.

Modern turbo-charged GA engines mated to carbs are almost unheard of. And if there are inter-coolers, you don't normally have controll over how much outside air they avail... it's all a "black box". You manage the whole deal by airspeed and manifold-pressure.

[snippyfsxer]

Thanks for the great explanations, guys.  I've been looking for the Carb Heat lever on the Beech Duke, but that explains it!

[BSW727]

[quote][quote][quote]Yeah..

[Brett_Henderson]

I was taught to cancel carb-heat on short final.. If you've had it applied since intitial, landing power-reduction..  no ice will form during that last 1/4 mile.. and having that extra 200RPM for go-around power, can make the difference between climbing out, and slamming into the runway..

Also..  don't retract the flaps until you're out of ground-effect and at Vy.

[BSW727]

They didn't want us touching it on short final because after the increase in RPM from pushing it in, you then have to make a power, and or pitch adjustment to maintain the rate of descent.

You still have plenty of power in reserve with the carb heat out for a go-around. You're only holding around 1300 to 1600 RPM for the descent depending on conditions.

Different syllabusses and instructors will have different procedures I guess.

Tough to climb at 67KIAS at 30 flaps. 

[Brett_Henderson]

Yeah.. different techniques ..

Though I'd much rather adjust my approach for a little extra RPMs.. than compromise my aborted landing by even more RPMs.


[quote]Tough to climb at 67KIAS at 30 flaps.

[DaveSims]

[quote]Yeah.. different techniques ..

Though I'd much rather adjust my approach for a little extra RPMs.. than compromise my aborted landing by even more RPMs.


[quote]Tough to climb at 67KIAS at 30 flaps.

[Brett_Henderson]

There are arguments for either technique.. except I think that we're talking about different "go-arounds".

I always considered a decision to abort a landing before in ground-effect, as nothing more than a transition from descent to climb. You're still well above stall-speed, and still well above the ground. There's nothing urgent or critical about it.

Now, the critical go-around is where decisions and timing mean the difference between airplanes (an occupants), getting damaged. Imagine a wind-gust as you're flaring..